1. Field of the Invention
This invention relates to opto-electronic couplers and more particularly to a circuit arrangement using such couplers between circuits of differing potential.
2. Description of the Prior Art
The family of electronic circuit elements has been enriched within the last few years due to the addition of an electronic relay which is comprised of a light-emitting diode optically coupled to a light-sensitive receiver placed within a housing. These electronic component elements are mentioned in the technical literature as opto-electronic couplers, photocouplers, photo-coupled pairs, optical insulators, or, in short hand form, optocouplers. These otptocouplers are increasingly used in many fields of electrical engineering since they provide an ideal separation for circuits between which a high potential difference exists. Since the optocouplers do not contain any moveable parts or other elements which are subject to wear, a long life will result, even when operated in severe environments. The optocouplers may serve as non-mechanical commutators, switches, and logical switch elements, as well as for connecting data recorders, card punchers, typewriters or other peripheral devices to a computer system without causing undesirable interference in the computer due to such connections.
Optocouplers may basically operated in two modes: in pulse operation or in linear operation. With the first mode of operation, it is possible to drive a luminous diode provided in the excitor circuit of an optocoupler with the use of a pulsed or alternating current. As a result, alternating or pulsing light waves are emitted which impact upon a phototransistor operating as a radiation receiver. Corresponding analogous components are used for a similar circuit operated with direct current in the input circuit. In the case of an optocoupler operated from direct current, however, there is the drawback that a signal potential is provided for operation of the photoreceiver, and, in the case of a defect in the photoreceiver, this signal potential simulates an unwanted logical value which is not related to the associated input signal. For example, when such circuits are used in the field of railroad safety or reactor control for coupling from key or relay contacts, care must be taken that the above-mentioned fault does not cause false signal indications.